Histochemical methods are being developed to demonstrate the presence in bovine photoreceptor outer segments of enzymes thought to be important in the process of photoreceptor outer segment renewal such as a galactosyltransferase which may be involved in the shedding of disc membranes and their subsequent phagocytosis by the pigment epithelium. Concurrent ultrastructural, autoradiographic and biochemical studies will be correlated with the histochemistry to demonstrate the function of outer segment enzymes.